Molecular sieve catalyst treatment

Abstract

Treatment at elevated temperature and advantageously superatmospheric pressure with an inert gas, especially nitrogen, rejuvenates molecular sieve catalysts deactivated by use in liquid-phase or supercritical or dense-phase olefin oligomerization, or by use in aromatic alkylation.

We claim: 
     
       1. A process for rejuvenating a molecular sieve catalyst, deactivated by use in a fixed bed olefin oligomerization process, the rejuvenation process comprises interrupting the oligomerization process after the temperature required to carry out the reaction under otherwise constant conditions has risen by at most 50 degrees C. and contacting the deactivated catalyst with a gas consisting essentially of nitrogen gas at an elevated temperature of at most 300° C. and at superatmospheric pressure for a time sufficient to effect an increase in olefin selectivity and catalytic activity of the deactivated catalyst; wherein the rejuvenated catalyst has a higher trimer selectivity than virgin catalyst. 
     
     
       2. The process according to  claim 1  wherein the molecular sieve comprises a compound selected from the group consisting of ZSM-22, ZSM-57, MCM-22, MCM-49 and mixtures thereof. 
     
     
       3. The process according to  claim 1  wherein rejuvenation is carried out at an elevated temperature in the range of from 100° C. to 300° C. 
     
     
       4. The process according to  claim 3  wherein the temperature is in the range of from 150° C. to 250° C. 
     
     
       5. The process according to  claim 1  wherein rejuvenation is carried out at a superatmospheric pressure in the range of from 150 kPa to 2 MPa. 
     
     
       6. The process according to  claim 5  wherein the pressure is in the range of from 500 kPa to 1 MPa. 
     
     
       7. The process according to  claim 1  wherein the rejuvenation pressure is at least 7.4 MPa and at most 10 MPa. 
     
     
       8. The process according to  claim 1  wherein the molecular sieve catalyst is deactivated by a feedstock contaminated with a compound selected from a sulphur compound, a nitrogen compound, and mixtures thereof. 
     
     
       9. A method for enhancing selectivity to trimer formation in an olefin oligomerization process under conditions selected from conditions whereby the feedstock is in the liquid phase and conditions whereby the feedstock is in the supercritical condition, comprising contacting the olefin feedstock with a molecular sieve catalyst that has been rejuvenated by the process according to  claim 1 . 
     
     
       10. A process for the oligomerization of an olefinic feedstock, which comprises contacting the feedstock under oligomerization conditions selected from the group consisting of conditions whereby the feedstock is in the liquid phase and conditions whereby the feedstock is in the supercritical condition, with a fixed bed of a molecular sieve catalyst that has been rejuvenated by the process according to  claim 1 . 
     
     
       11. The process according to  claim 10  which comprises repeating the cycle of reaction and rejuvenation at least one time. 
     
     
       12. The process according to  claim 1  wherein the trimer selectivity of the deactivated catalyst after rejuvenation is at least 75.0%. 
     
     
       13. The process according to  claim 1  wherein the trimer selectivity of the deactivated catalyst after rejuvenation is at least 77.0%. 
     
     
       14. The process according to  claim 1  wherein the trimer selectivity of the deactivated catalyst after rejuvenation is at least 77.6%. 
     
     
       15. The process according to  claim 1  wherein the gas is nitrogen gas.